Sandy soils of the arid/semiarid dune fields of the Palestinian Gaza Strip and the Israeli western Negev are extensively covered by biological soil crusts (BSC), which stabilize the surface and prevent desertification. Political discussions in Israel suggest transferring a large part of this sand belt to the Gaza Strip within a final peace accord. Inappropriate land uses may lead to destruction of the BSC and initiate desertification, as already occurring in parts of the Gaza Strip. In this interdisciplinary project the influence of environmental factors on the vitality, stability and the recovery potential of the BSC will be investigated in order to evaluate the carrying capacity of this fragile landscape, in relation to rainfall, soil and relief conditions. A transect stretching from the Mediterranean coast in the Palestinian Gaza Strip (370 mm rainfall) to 65 km southwards in Israel ( Nizzana , less than 100 mm rainfall) has been selected. The interactions of molecular biological, physiological, physical and soil chemical processes, expressed in specific characteristics of the BSC and the underlying soil, will be assessed from the molecular to the landscape scale.
Recent and predicted increases in extremely dry and hot summers emphasise the need for silvicultural approaches to increase the drought tolerance of existing forests in the short-term, before adaptation through species changes may be possible. We aim to investigate whether resistance during droughts, as well as the recovery following drought events (resilience), can be increased by allocating more growing space to individual trees through thinning. Thinning increases access of promoted trees to soil stored water, as long as this is available. However, these trees may also be disadvantaged through a higher transpirational surface, or the increased neighbourhood competition by ground vegetation. To assess whether trees with different growing space differ in drought tolerance, tree discs and cores from thinning experiments of Pinus sylvestris and Pseudotsuga menziesii stands will be used to examine transpirational stress and growth reduction during previous droughts as well as their subsequent recovery. Dendroecology and stable isotopes of carbon and oxygen in tree-rings will be used to quantify how assimilation rate and stomatal conductance were altered through thinning. The results will provide crucial information for the development of short-term silvicultural adaptation strategies to adapt forest ecosystems to climate change. In addition, this study will improve our understanding of the relationship between resistance and resilience of trees in relation to extreme stress events.
Water is an intrinsic component of ecosystems acting as a key agent of lateral transport for particulate and dissolved nutrients, forcing energy transfers, triggering erosion, and driving biodiversity patterns. Given the drastic impact of land use and climate change on any of these components and the vulnerability of Ecuadorian ecosystems with regard to this global change, indicators are required that not merely describe the structural condition of ecosystems, but rather capture the functional relations and processes. This project aims at investigating a set of such functional indicators from the fields of hydrology and biogeochemistry. In particular we will investigate (1) flow regime and timing, (2) nutrient cycling and flux rates, and (3) sediment fluxes as likely indicators. For assessing flow regime and timing we will concentrate on studying stable water isotopes to estimate mean transit time distributions that are likely to be impacted by changes in rainfall patterns and land use. Hysteresis loops of nitrate concentrations and calculated flux rates will be used as functional indicators for nutrient fluxes, most likely to be altered by changes in temperature as well as by land use and management. Finally, sediment fluxes will be measured to indicate surface runoff contribution to total discharge, mainly influenced by intensity of rainfall as well as land use. Monitoring of (1) will be based on intensive sampling campaigns of stable water isotopes in stream water and precipitation, while for (2) and (3) we plan to install automatic, high temporal-resolution field analytical instruments. Based on the data obtained by this intensive, bust cost effective monitoring, we will develop the functional indicators. This also provides a solid database for process-based model development. Models that are able to simulate these indicators are needed to enable projections into the future and to investigate the resilience of Ecuadorian landscape to global change. For the intended model set up we will couple the Catchment Modeling Framework, the biogeochemical LandscapeDNDC model and semi-empirical models for aquatic diversity. Global change scenarios will then be analyzed to capture the likely reaction of functional indicators. Finally, we will contribute to the written guidelines for developing a comprehensive monitoring program for biodiversity and ecosystem functions. Right from the beginning we will cooperate with four SENESCYT companion projects and three local non-university partners to ensure that the developed monitoring program will be appreciated by locals and stakeholders. Monitoring and modelling will focus on all three research areas in the Páramo (Cajas National Park), the dry forest (Reserva Laipuna) and the tropical montane cloud forest (Reserva Biologica San Francisco).
During microbial turnover of organic chemicals in soil, non-extractable residues (NER) are formed frequently. Studies on NER formation usually performed with radioisotope labelled tracer compounds are limited to localisation and quantitative analyses but their chemical composition is left unknown. Recently, we could show for 2,4-dichlorophenoxyacetic acid and ibuprofen that during microbial turnover in soil nearly all NER were derived from microbial biomass, since degrading bacteria use the pollutant carbon for their biomass synthesis. Their cell debris is subsequently stabilised within soil organic matter (SOM) forming biogenic NER (bioNER). It is still unknown whether bioNER are also formed during biodegradation of other, structurally different compound classes of organic contaminants. Therefore, agricultural soil will be incubated with labelled compounds of five classes of commonly used and emerging pesticides: organophosphate, phenylurea, triazinone, benzothiadiazine and aryloxyphenoxypropionic acid. The fate of the label will be monitored in both living and non-living SOM pools and the formation of bioNER will be quantified for each compound over extended periods of time. In addition, soil samples from long-term lysimeter studies with 14C-labelled pesticide residues (e.g. triazine, benzothiazole and phenoxypropionic acid group) will be also analysed for bioNER formation. The results will be summarised to identify the metabolic conditions of microorganisms needed for bioNER formation and to develop an extended concept of risk assessment including bioNER formation in soils.
Dissolved organic matter (DOM) is one major source of subsoil organic matter (OM). P5 aims at quantifying the impact of DOM input, transport, and transformation to the OC storage in the subsoil environment. The central hypotheses of this proposal are that in matric soil the increasing 14C age of organic carbon (OC) with soil depth is due to a cascade effect, thus, leading to old OC in young subsoil, whereas within preferential flowpaths sorptive stabilization is weak, and young and bioa-vailable DOM is translocated to the subsoil at high quantities. These hypotheses will be tested by a combination of DOC flux measurements with the comparative analysis of the composition and the turnover of DOM and mineral-associated OM. The work programme utilizes a DOM monitoring at the Grinderwald subsoil observatory, supplemented by defined experiments under field and labora-tory conditions, and laboratory DOM leaching experiments on soils of regional variability. A central aspect of the experiments is the link of a 13C-leaf litter labelling experiment to the 14C age of DOM and OM. With that P5 contributes to the grand goal of the research unit and addresses the general hypotheses that subsoil OM largely consists of displaced and old OM from overlying horizons, the sorption capacity of DOM and the pool size of mineral-associated OM are controlled by interaction with minerals, and that preferential flowpaths represent 'hot spots' of high substrate availability.
Soil microorganisms can mobilize and immobilize phosphorus (P), and therefore strongly affect the availability of P to plants. In this project we hypothesize that the ratio of labile P to microbial P increases during the transition from acquiring to recycling ecosystems. Microbial and plant P uptake will be studied with 33P that will be quantified in microbial and plant biomass as well as in lipids. To what extent microorganisms immobilize and mobilize P during decomposition of soil organic matter will be explored with a 14C/33P labeled monoester. Seasonal dynamics of actual and potential P mineralization (33P dilution and phosphatase activity), and microbial P immobilization will be studied with soils of the transition from acquiring to recycling ecosystems. The contribution of litter-derived P will be explored in a litter exclusion experiment in the field. Spatial patterns of microbial and plant P mineralization in the rhizosphere will be explored by analyses of areas of high acid and alkaline (=microbial-derived) phosphatase activity by soil zymography, and their relations with areas of high rhizodeposition (14C imaging). In conclusion, we will analyse mechanisms of actual and potential microbial P mineralization and immobilization, localization, and consequences for P uptake by plants.
The geomagnetic field shields our habitat against solar wind and radiation from space. Due to the geometry of the field, the shielding in general is weakest at high latitudes. It is also anomalously weak in a region around the south Atlantic known as South Atlantic Anomaly (SAA), and the global dipole moment has been decreasing by nearly 10 percent since direct measurements of field intensity became possible in 1832. Due to our limited understanding of the geodynamo processes in Earths core, it is impossible to reliably predict the future evolution of both dipole moment and SAA over the coming decades. However, lack of magnetic field shielding as would be a consequence of further weakening of dipole moment and SAA region field intensity would cause increasing problems for modern technology, in particular satellites, which are vulnerable to radiation damage. A better understanding of the underlying processes is required to estimate the future development of magnetic field characteristics. The study of the past evolution of such characteristics based on historical, archeo- and paleomagnetic data, on time-scales of centuries to millennia, is essential to detect any recurrences and periodicities and provide new insights in dynamo processes in comparison to or in combination with numerical dynamo simulations. We propose to develop two new global spherical harmonic geomagnetic field models, spanning 1 and 10 kyrs, respectively, and designed in particular to study how long the uninterrupted decay of the dipole moment has been going on prior to 1832, and if the SAA is a recurring structure of the field.We will combine for the first time all available historical and archeomagnetic data, both directions and intensities, in a spherical harmonic model spanning the past 1000 years. Existing modelling methods will be adapted accordingly, and existing data bases will be complemented with newly published data. We will further acquire some new archeomagnetic data from the Cape Verde islands from historical times to better constrain the early evolution of the present-day SAA. In order to study the long-term field evolution and possible recurrences of similar weak field structures in this region, we will produce new paleomagnetic records from available marine sediment cores off the coasts of West Africa, Brazil and Chile. This region is weakly constrained in previous millennial scale models. Apart from our main aim to gain better insights into the previous evolution of dipole moment and SAA, the models will be used to study relations between dipole and non-dipole field contributions, hemispheric symmetries and large-scale flux patterns at the core-mantle boundary. These observational findings will provide new insights into geodynamo processes when compared with numerical dynamo simulation results.Moreover, the models can be used to estimate past geomagnetic shielding above Earths surface against solar wind and for nuclide production from galactic cosmic rays.
The vegetation of East and South African savannahs has been shaped by the complex interaction of geo-biophysical processes and human impact. For both regions a controversial discussion is pertinent, as to whether massive degradation threatens the sustainability of livelihoods in these regions. Rangeland vegetation is mainly affected by environmental conditions (soil and climate) and by livestock management. Extent and interaction of these drivers are not well understood but have profound impacts on the resilience and vulnerability of these systems to be shifted toward unfavourable degraded or bush encroached states. The project aims to analyse and model rangeland vegetation in response to range management including livestock, soil quality and climatic conditions and to assess the impacts of changes in these conditions on the resilience and vulnerability of rangeland systems. Field measurements, remote sensing of vegetation patterns and dynamics and simulation modelling will be used to understand the dynamics of rangeland vegetation. We will use the 'fast' or 'state' variables potential of pastures to produce palatable biomass, the variability of this production, and the system's potential to recover from disturbance impact as indicators of resilience. 'slow' variables that control (or drive) the 'fast' variables such as management, climate and soil variables are recorded in cooperation with other subprojects as with A1 for soil variables. Results of the project will show which management activities are most favourable for individual regions to sustain plant production in the long term.
The formation of biogeochemical interfaces in soils is controlled, among other factors, by the type of particle surfaces present and the assemblage of organic matter and mineral particles. Therefore, the formation and maturation of interfaces is studied with artificial soils which are produced in long-term biogeochemical laboratory incubation experiments (3, 6, 12, 18 months. Clay minerals, iron oxides and charcoal are used as major model components controlling the formation of interfaces because they exhibit high surface area and microporosity. Soil interface characteristics have been analyzed by several groups involved in the priority program for formation of organo-mineral interfaces, sorptive and thermal interface properties, microbial community structure and function. Already after 6 months of incubation, the artificial soils exhibited different properties in relation to their composition. A unique dataset evolves on the development and the dynamics of interfaces in soil in the different projects contributing to this experiment. An integrated analysis based on a conceptual model and multivariate statistics will help to understand overall processes leading to the biogeochemical properties of interfaces in soil, that are the basis for their functions in ecosystems. Therefore, we propose to establish an integrative project for the evaluation of data obtained and for publication of synergistic work, which will bring the results to a higher level of understanding.
During the first project period we developed a general approach to quantify soil pore structure based on X-ray micro-tomography Vogel et al. (2010) which is applicable at various scales to cover soil pores larger that 0.05 mm in a representative way. Based on this method we generated equivalent network models to numerically simulate flow and transport of dissolved chemicals. The existing network model was extended to handle reactive transport and infiltration processes which are especially critical for matter flux in soil. The results were compared to experimental findings. The original research question 'what does a particle see on its way through soil' could be answered quantitatively for various boundary conditions including steady state flux and infiltration. However, we identified various critical aspects of the proposed modeling concept which will be in the focus of the second period. This includes 1) the spatial arrangement of interfaces having different quality which is crucial for chemical interactions and pore scale water dynamics, 2) the realistic multiphase dynamics at the pore scale which need to reflect the dynamic pressure and movement of trapped non-wetting phase and 3) the parametrization of structural complexity which need to be developed beyond the measurement of continuous Minkowski functions to allow the development of quantitative relations between structure and function. These aspects will be explored in a joint experiments in cooperation with partners within the SPP.
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